1. Field of the Invention
The present invention relates generally to liquid crystal displays and, more particularly, to a liquid crystal display having a customizable viewing envelope.
2. Description of the Related Art
Liquid crystal displays (LCDs) may be utilized in a variety of applications such as notebook computers, hand-held calculators, and wristwatches. LCDs are also used in many applications having relatively high optical performance specifications, e.g., precision instrumentation utilized in avionics. Different applications may have different optical performance requirements, such as minimum contrast ratio characteristics over a range of horizontal and/or vertical viewing angles. Although several prior art LCDs address the needs of individual applications, such solutions are typically expensive to implement and/or limited to a narrow field of use.
For example, referring to FIG. 1, a conventional polarized display 2 includes a front polarizer 8, a first substrate 11, a liquid crystal layer 12, a second substrate 14, and a rear polarizer 16 sandwiched between a cover glass 4 and a backlight 18. Each of the substrates 11, 14 suitably includes an alignment layer on the surface facing the liquid crystal 12 which is rubbed in a selected direction to facilitate the alignment of the liquid crystal molecules. Typically, the alignment layers are rubbed in directions that are at right angles to each other, for example at 135 degrees from a horizontal axis of the display on the first substrate 11 and at xe2x88x92135 degrees from the horizontal axis on the second substrate 14.
Light from the backlight 18 is initially polarized along a polarization axis of the rear polarizer 16, and electrical fields applied to portions of the liquid crystal cause the liquid crystal to either alter or preserve the polarization of light passing through the liquid crystal. Only light polarized along the polarization axis of the front polarizer 8 is transmitted.
The viewing envelope of a conventional display is typically limited. For example, referring to FIGS. 2A-C, the viewing envelope in both the horizontal and vertical directions deteriorates rapidly as the viewing angle deviates from the perpendicular. Consequently, the display is unsuitable for applications requiring an extended vertical or horizontal viewing envelope.
For applications requiring high contrast at angles other than the perpendicular, some displays include a negative birefringence retarder in the optical path of the display. The retarder tends to horizontally shift the viewing envelope, as shown in FIGS. 3A-C. Although the contrast on one side of the display improves, the contrast on the other side diminishes. In addition, the retarder tends to adversely affect the vertical viewing envelope.
Many applications, such as cockpit instrumentation, require relatively wide horizontal viewing angles and high contrast ratios. For example, the horizontal range requirements for some LCDs may be up toxc2x160 degrees. Other applications may require expanded vertical viewing envelopes or selected vertical viewing angles which cannot be adequately accommodated by conventional displays. For example, if an LCD is mounted in a predetermined position within an instrument panel, a vertical viewing angle range may be determined from the anticipated line of sight of the pilot and/or co-pilot. To facilitate acceptable display contrast for different vertical viewing angles, some prior art solutions utilize physically adjustable LCDs or instrument panels mounted with a swivel element. Such movable displays, however, are associated with many problems, including wear on moving parts, spatial requirements, and mounting.
A display according to various aspects of the present invention comprises an LCD having a first substrate, a second substrate proximate the first substrate, a liquid crystal material located between the first and second substrates, an element for compensating for horizontal view angle limitations of the display. The LCD may further include a nonmechanical element for vertically shifting the viewing angle associated with the high-contrast viewing envelope of the LCD device.